#include <stdio.h>

int main(int argc, char *argv[])
{
    int input_num = 0;
    int res = 0;
    printf("Please input:");

    scanf("%d", &input_num);


    if (input_num <= 2) {
        printf("1\n");
        return 0;
    }

    int before = 1;
    int before_before = 1;
    for (int i = 3; i <= input_num; i++) {
       res = before + before_before;
       before_before = before;
       before = res;
    }

    printf("%d\n", res);

    return 0;
}
